Optically Stimulated Luminescence Chronology And Paleo-environmental Implications Of Yardangs In The Qaidam Basin

Yardang landform in the Qaidam Basin is significant for understanding the paleo-environmental history and aeolian process,and a terrestrial analogue for Mars.However,their formation ages,indicating a transition from lake to wind erosion,are still unclear.Optically Stimulated Luminescence?OSL?chronology is applied in this paper to establish a chronological model to make clear yardang evolution in the Qaidam Basin,as well as its relationship to the source of Chinese Loess Plateau?CLP?.With global analyses,the driving mechanism and geomorphological model of yardang fields are revealed,which play a key role in researches of Martian yardangs.Dating methodological results show that:?1?With a sufficient bleaching and negligible anomalous fading,MET-p IRIR₂₅₀ could offer reliable ages using either fine-grain polyminerals or coarse-grained K-feldspars,and has a high saturation level of over1200 Gy;?2?However,p IR₅₀IR₂₅₀ suffer from anomalous fading,and their corrections may need more evaluation,especially for the old samples?>700-800 Gy?;?3?D_es of p IR₂₀₀IR₂₅₀ are consistent with MET-p IRIR₂₅₀,suggesting its feasibility in this study.Considering the signal intensity and dating range,MET-p IRIR₂₅₀,p IR₂₀₀IR₂₅₀ and quartz OSL were selected to establish the dating framework.A combination of quartz OSL and feldspar p IRIR methods built a chronological model since?350 ka in the east basin,but,in the west basin,it is out of dating range.The geomorphological and environmental significance of yardangs since the middle-late Pleistocene in Qaidam Basin are as follows:?1?Spatial domain:yardangs in the west basin are developed earlier than that in east basin,but they are still in the juvenile-mature stage;however,yardangs in the east basin has entered the mature-demise stage.This is because the strong wind in the west basin provides continuous downcutting,which continuously updates the"basement"of the yardang long-ridges.However,in the east basin,downcutting is limited and the lateral erosion is enhanced,leading to yardang demise.?2?Temporal domain:yardangs are mainly developed in the glacial periods,while lakes are dominant in the interglacial periods.During glacial periods,the strengthened westerlies is moved to anchor over the Qaidam Basin,accelerating yardang development.During interglacial periods,the enhanced Asian summer monsoon brings more precipitation to the basin,maintaining paleolake development.?3?The last yardangs in the Qarhan area of east basin resumed in Marine Isotopic Stage?MIS?6,especially MIS 4,and have evolved into a streamline form in MIS 2.The MIS 5 lake would submerge some yardangs of MIS 6.Within a unidirectional wind,increased lateral erosion and a high salinity environment,linear yardangs were developed during MIS 4-2.After Last Glacial Maximum,the aeolian sands are accumulated,which inherited the linear form of yardangs and developed into the linear dune.?4?The model of"yardangs alternated with lakes"provides new evidence for that Qaidam Basin is an important source for the CLP.A large amount of dust will be released during yardang development during glacial periods,and transported by the strong wind.Abundant lacustrine sediments in the basin provide a sustainable supply of dust.Further analyses of the distribution,age,climatic and geologic condition of yardangs worldwide suggest a climate-driven mechanism for yardangs.Controlled by the westerlies mostly,yardang development could be accelerated during the glacial periods when the dry and powerful westerlies is shifted toward equator as changes in atmospheric circulation;but interrupted by lake accumulations during wet-warm interglacial periods,at least for the last ice age.Depressions could be created or enlarged in yardang fields in glacial periods,and then,would be developed into lakes during interglacial periods,which can be evolved into new yardangs in the following glacial periods,revealing the alternation of yardangs and lakes geomorphologically.In addition,utilizing the rules of Earth-based yardang evolution,we can identify the specific level of yardang development and explore the geomorphological processes as well as the climatic background for yardang fields on Mars.